The favourite jokes of mum and I when I was a kid:

Q: Why is a duck with a tin lip?
A: Because the higher they fly, the fewer.

Q: What is the difference between a duck?
A: One of its legs is both the same.

Other favourites:

Q: Why did the boy fall off his bike?
A: Someone threw a fridge at him.

Q: What's red, goes around in circles, and taps on the glass?
A: Baby in a microwave.

Q: What's worse than ten babies in a garbage bin?
A: One baby in ten garbage bins.